1. Field of the Invention
One aspect of the present invention relates to a vacuum brake booster and a method of operation of a vacuum brake booster of a vehicle brake system.
2. Description of the Related Art
Vacuum brake boosters are employed in order to boost the brake force exerted by the driver at the brake pedal. The vacuum brake booster consists of at least two chambers exhibiting a difference in pressure. These chambers are the working chamber and the vacuum chamber, which are integrated into the brake system in such a fashion that the working chamber is connected to the atmosphere. The vacuum chamber is bled by means of a vacuum supply. Both chambers are separated by a diaphragm. The vacuum furnished by the internal combustion engine or a vacuum pump boosts the pedal force that is to be applied by the driver. Depending on the available vacuum, a condition is reached with defined pedal forces, which renders further increase of the force on the actuating unit possible only by an increase in the pedal force since the vacuum brake booster has reached the maximum possible boosting force. This condition is referred to as the operating point of the vacuum brake booster.
WO 2006/092348 A1 discloses a method for detecting the control point of a vacuum booster. In the prior art method, the pressure prevailing in the vacuum chamber is measured by means of a pressure sensor, and the control point is calculated with the aid of a mathematical function solely on the basis of the pressure prevailing in the vacuum chamber. It is intended according to the prior art method that the control point is detected when the pressure signal of the pressure sensor exhibits a minimum. The question whether the signal of the single pressure sensor is secured or reliable is not dealt with.
In view of the above, one aspect of the invention involves improving the method described hereinabove in such a manner that operation of a vacuum brake booster with only one pressure sensor is reliable and safe.